Folia Malacol. 29(2): 117–120

https://doi.org/10.12657/folmal.029.012

NON-NATIVE HELIX LUCORUM LINNAEUS, 1758 (GASTROPODA: EUPULMONATA: HELICIDAE) AFTER TWELVE YEARS IN PRAGUE, CZECH REPUBLIC

Jiři Doležal

Verdunská 25, Praha 6, Czech Republic (e-mail: [email protected]); https://orcid.org/0000-0001-8402-6125 Abstract: The first occurrence of Helix lucorum Linnaeus in the Czech Republic was reported 12 years ago, at the closed train station Žižkov in Prague. A part of the station is a ruderal habitat while large patches are covered with partly damaged concrete. At the site where it was first recorded, and where the density of H. lucorum is still the highest, this invasive snail has now almost completely replaced the original H. pomatia Linnaeus. However, it has not expanded either inside or outside the station area. Key words: invasive species; Helix lucorum; Prague; Czech Republic

INTRODUCTION

Helix lucorum Linnaeus, 1758 (Eupulmonata, ern snails. Over the last thirty years, the number of Helicidae) is an invasive species. It was first recorded non-native species of terrestrial snails in the Czech in Prague in 2008, within the urban heat island, at Republic has increased from 5 to 15 (8% of all spe- the closed train freight station Žižkov (Horsák et cies); more than half of them are of Mediterranean al. 2010). The species was reported from the same origin. Since 2000, seven new non-native species (six locality four (Peltanová et al. 2012a) and ten years of them Mediterranean) have been recorded. This later (Korábek et al. 2018). Currently, H. lucorum is trend reflects the global warming and the increase included in the Czech Republic check-list and in the in the intensity of foreign trade over the past six dec- distribution maps of the molluscs of the Czech and ades, suggesting a synergistic effect of climate condi- Slovak Republics (Horsák et al. 2021). tions and socio-economic factors on snail expansion The species is native to Anatolia, and to the south- (Peltanová et al. 2012b). ern and eastern Balkans; at present it is widespread H. lucorum is spreading throughout Europe. It in southern Europe, with the range extending from was recorded, among other countries, in Hungary Spain to eastern Turkey (Welter-Schultes 2012). (Varga et al. 2010), in Slovakia (Čejka & Čačaný It is assumed that it does not form subspecies. The 2014) and in Russia (Moscow; Egorov 2017). The Crimean form of H. lucorum is not regarded as a sub- aim of this study was to check if the local popula- species, but as a conchologically distinct population tion of H. lucorum, recorded for the first time 12 years (Korábek et al. 2018). ago, had spread from its initial locality at the closed The reported expansion of H. lucorum reflects the railway station Žižkov and expanded to the nearby general trend of northward spread of originally south- green areas.

MATERIAL AND METHODS

The closed railway station Žižkov is surrounded on its eastern side it is connected to the nearby un- by walls and busy asphalted roads, but at one point developed areas by a strip of wasteland (Fig. 1), with 118 Jiři Doležal

Fig. 1. Closed railway station Žižkov. The station boundary indicated with large white dots. The wide white line denotes the potential bio-corridor. Sites A–F indicated in red. The patch with high density of H. lucorum marked with small white dots. Yellow dots mark searched spots within and outside the station. Inset shows a map of Prague’s heat island (Český hydrometeorologický ústav 2010), white dot in its centre – Žižkov railway station soil only sparsely covered with herbage along the son, the soil, especially around site A, is covered with railway tracks (not used for decades). This strip of dense leaves of herbs, and the snails are difficult to undeveloped land may serve as a bio-corridor. find. After the leaves have fallen, it is much easier To monitor the spread of H. lucorum, I used the to find empty shells. In the spot where I observed Mumladze method which I modified (Mumladze (in both summer and winter) the highest density of 2013). During a tour in September 2018, in the cen- H. lucorum (site A), I collected all the empty shells tre of the Žižkov station, I found a spot which was of Helix from a 10 × 10 metres plot, and counted favourable for molluscs. Most of the station’s space the number of shells of H. lucorum and H. pomatia is concrete-covered. Snails can only be found in a few Linnaeus, 1758. places where the vegetation patches are close to the I used the same method in the other sites, and crumbling buildings and the terrain tends to be rug- collected all the shells of the genus Helix from ged. At site A, in the summer I found a high density 10 × 10 metres plot in each. I also chose one place of snails, not only H. lucorum, but also smaller helic- (a recently abandoned landfill) outside the station – ids, such as the common Cepaea nemoralis (Linnaeus, site F. Besides, I searched the entire area of the sta- 1758). tion and its close surroundings (not only sites A–E Other collections took place during the dormant and F) and collected shells of the genus Helix during period from the beginning of winter to early spring, the winter/early spring between 2018 and 2021. when the soil was visible. During the growing sea-

RESULTS Table 1. Numbers of Helix shells found in the surveyed sites During its 12 years of occurrence, H. lucorum Site Geographical coordinates H. pomatia H. lucorum spread neither through the closed station, nor out- A 50°05.06'N, 14°28.63'E 6 83 side it (Fig. 1). It was only found in larger numbers B 50°05.03'N, 14°28.34'E 4 12 in a patch of a few hundred square metres (site A C 50°05.11'N, 14°28.86'E 2 4 and nearby). In this area, it significantly outnum- D 50°05.17'N, 14°28.74'E 0 1 bered the native H. pomatia. The numbers of shells E 50°05.13'N, 14°28.66'E 0 1 of H. lucorum and H. pomatia in the surveyed sites are F* 50°05.15'N, 14°29.20'E 20 0 shown in Table 1. * – outside the station. Helix lucorum in Prague, Czech Republic 119

DISCUSSION

There are at least four mechanisms of passive ature and the temperature of the substratum (Voss dispersal of terrestrial molluscs: anemochory, hydro- et al. 2001). This may limit the accessibility of the chory, zoochory and anthropochory (Kramarenko bio-corridor to snails and thus explain the absence of 2014). The expansion involves two distinct spa- any Helix in certain parts of the station. In the north- tial scales: transcontinental and intra-continen- ern and eastern parts of the station large patches of tal. Most transcontinental expansions are cases of concrete cover the ground; they may cause frequent spread of European species to Africa, the Americas temperature differences between air and subsoil. and Australia. Outside Europe, H. lucorum was The population of H. lucorum lives only in a narrow, found in North America, northern Africa and China broken strip of greenery, but it does not spread even (GBIF Secretariat 2019). It was also recorded in within the area, where there are no physical barri- Uzbekistan (Izzatulayev 2013). In Europe this syn- ers to dispersal. Therefore, the dry substrate in most anthropic species, besides accidental passive disper- of the area can be regarded as a very likely limiting sal, was also introduced intentionally for commercial factor. A long dry strip of land in the eastern end of purposes and now it is regarded as one of the most the station, of about two hundred and fifty metres, conspicuous snail newcomers in Eastern, Central and apparently prevents H. lucorum from penetrating the Western Europe (Mienis & Rittner 2010, Korábek potential bio-corridor with wet vegetation along the et al. 2018). Its colonies in Prague and Moscow sur- railway tracks. This indicates that the expansion-pre- vived inside the city heat islands (Egorov 2017). venting factors are rather local, associated with the Now it is common in Budapest where the popula- microclimate of the locality. H. lucorum should still be tions were established in the last 30 years (Páll- regarded as a potentially invasive species. Gergely et al. 2019). In France, besides the heat island of Paris, H. lucorum occurs in the south of the ACKNOWLEDGEMENTS country (Muséum national d’Histoire naturelle (Ed.) 2003–2021). In northern Greece the activi- I would especially like to thank Associate Professor ty of H. lucorum is primarily controlled by humidity, Lucie Juřičková (Charles University, Prague, Czech while temperature and photoperiod affect the activity Republic) for a very kind repeated consultation, only when days are long and cool or short and hot when she gave me, albeit a layman, her time and an- (Lazaridou-Dimitriadou & Saunders 1986). swered my probably very stupid questions. She also Although the introduced population of H. lucorum informed me about the colony of H. lucorum in Prague. has inhabited the locality for twelve years and it now I would also like to thank Associate Professor Levan outnumbers the native H. pomatia, it is not expand- Mumladze (Ivane Javakhishvili State University, ing any further, therefore in Prague it currently does Tbilisi, Georgia) for his kind consultations and ex- not meet the criteria of an invasive species. planations of his work on H. lucorum, which was a H. pomatia was found to prefer habitats with the valuable guide to me and whose method I used. smallest possible difference between the air temper-

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